Artificial muscle could help robots mimic biology

A self-contained soft actuator, which performs in a similar way to natural muscle, could signal a breakthrough in soft robotics.
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The artificial muscle in use as a bicep lifts a skeleton’s arm to a 90 degree position. Photo: Aslan Miriyev/Columbia Engineering

A self-contained soft actuator, which performs in a similar way to natural muscle, could signal a breakthrough in soft robotics.

A team from Columbia Engineering in New York City has developed a 3D-printable synthetic soft muscle with intrinsic expansion ability that does not require an external compressor or high voltage equipment as previous muscles required.

The new material can lift 1000 times its own weight and has a strain density (expansion per gram) that is 15 times larger than natural muscle.

“We’ve been making great strides toward making robot minds, but robot bodies are still primitive,” said Hod Lipson, a professor of mechanical engineering in the Creative Machines lab at Columbia.

“This is a big piece of the puzzle and, like biology, the new actuator can be shaped and reshaped a thousand ways. We’ve overcome one of the final barriers to making lifelike robots.”

He said, until now no material has been capable of functioning as a soft muscle due to an inability to exhibit the desired properties of high actuation stress and high strain. Existing soft actuator technologies are typically based on pneumatic or hydraulic inflation of elastomer skins that expand when air or liquid is supplied to them. The external compressors and pressure-regulating equipment required for such technologies prevent miniaturisation and the creation of robots that can move and work independently.

To achieve this actuator, the team used a silicone rubber matrix with ethanol distributed throughout in micro-bubbles. The solution combined the elastic properties and extreme volume change attributes of other material systems while also being easy to fabricate, low cost, and made of environmentally safe materials.

After being 3D-printed into the desired shape, the artificial muscle was electrically actuated using a thin resistive wire and low-power (8 V). It was tested in a variety of robotic applications where it showed significant expansion-contraction ability, being capable of expansion up to 900% when electrically heated to 80°C. Via computer controls, the autonomous unit is capable of performing motion tasks in almost any design.

Further developments will include: incorporating conductive materials to replace the embedded wire; accelerating the muscle’s response time; and increasing its shelf life. And in the long-term, they will involve artificial intelligence to learn to control the muscle, with the goal of replicating natural motion.

[The artificial muscle in use as a bicep lifts a skeleton’s arm to a 90 degree position. Photo: Aslan Miriyev/Columbia Engineering]